Which is the path to particle drivers data? (Blender Python API)
An emitter object emits particles. It does not have any drivers associated with it that it passes onto particles. When it emits objects, the objects it emits as particles can have drivers.

You need to be looking in the original objects for the drivers, each object gets duplicated as a particle - the drivers the particles use are duplicated from the original object.

&gt;&gt;&gt; bpy.data.objects['Sphere.048'].animation_data.drivers[0].driver.expression
'randf(0.25,0.9)'


As far as the existence of particle_systems[0].particles[0].driver_add() goes, I expect it only exists as an inherited function from the base class, same as keyframe_insert, items, keys... To add a driver to an individual particle would mean it only exists during the particles lifetime, meaning you would need to add the driver as each particle is created. The properties you can access from each particle object is only relevant to a particles existence, so I also expect that most of these values are 'driven' by the particle system and will not actually work with drivers.